Many circuit boards designed to operate in the microwave range of frequencies are implemented using microstrip circuitry. Microstrip circuits are characteristically difficult to test because the circuit must be designed to include points at which a test probe can be accepted, and it has been the case that these test points themselves have had a measurable effect on the operation of the circuit.
Special provisions must be made to accommodate measurement of the electrical parameters of a signal being carried by a microstip circuit. Such special provisions have included power dividers or directional couplers. In many circuits of this type, it is necessary to be able to monitor a wide range of frequencies so that if a directional coupler is used for this purpose, the directional coupler will occupy a relatively large area on the circuit board. In the design of such circuits, size and weight are always at a premium and consequently, the space is frequently not available for the desired test points. Wide band resistive power dividers have been used as well. These are smaller, but they introduce at least a 6 db insertion loss in the circuit being tested.
It is therefore, an object of this invention to provide a radio frequency test probe device for microstrip circuitry that is usable over a very wide frequency range, such as, for example, DC to 18 GHz.
Another object of this invention is to provide such a test probe and an arrangement for accommodating the test probe on a microstrip circuit board which will require that very little of the circuit board area be used for purposes of accommodating the probe's requirements.
Still another object of this invention is to provide a test probe arrangement of the foregoing variety which introduces very low loss in the circuit being tested when in operation and no loss when not in use.